The invention relates to a spectrometer for the simultaneous measurement of several spectral lines of a sample with several wavelength selectors each selectively supplying light of a certain wavelength to a detector, wherein usually each wavelength selector selects a different wavelength.
A multiple channel spectrometer of this type is e.g. supplied by the company Bruker AXS GmbH (see manual "Mehrkanal-Ro ntgenstpektrometer MRS 4000" dated 1997).
In order to examine the optical characteristics of samples, in particular for determining the chemical composition on the basis of specific, optical characteristics of the different atoms and molecules, a multitude of most different spectrometers is used which operate in wavelength ranges from the far-infrared via the visible range to the range of X-rays. In all these spectrometers the sample to be examined is irradiated with light of one or several wavelengths and the light modified by the sample, being characteristic of the sample, is detected either in transmission or reflection and is evaluated in the form of a spectrum.
To obtain spectral resolution of the detected measuring signals, up to now two alternative methods have been used, i.e. the use of an energy-dispersive or a wavelength-dispersive arrangement.
An energy-dispersive spectrometer usually comprises only one single detector which directly receives the radiation to be examined from the sample. Since the detector "faces the sample directly" it does not only receive the interesting "useful radiation" but also the entire background and interfering radiation. In particular, often the detector will be highly influenced by the radiation of the main elements which sometimes are of no interest whatsoever since they are known anyway. In this manner, the signals of the actually interesting elements disappear inside the strong background or interference signals. As a consequence, an energy-dispersive spectrometer of this type has only low resolution and a high detection limit and therefore a relatively low overall performance.
As an alternative, wavelength-dispersive spectrometers are used, like e.g. the initially cited multiple channel X-ray spectrometer "MRS 4000". These devices comprise a multitude of analyzers and detectors, wherein each element to be measured has its own analyzer crystal and its own detector. In this manner, it is possible to receive the signals of various wavelengths simultaneously. The wavelength-dispersive spectrometers are thus very powerful and have a high resolution.
However, the big effort required owing to the many detectors and associated measuring electronics for each wavelength range and the increased vulnerability to disturbances due to the multitude of highly sensitive components is a disadvantage. In particular, the required large number of detectors and independent measuring electronics associated therewith render such spectrometers quite expensive.
WO 97/05474 on the other hand discloses a wavelength-dispersive X-ray fluorescence spectrometer which provides for several analyzers operating in different wavelength ranges with only one single detector. However, this spectrometer does not allow simultaneous measurements of light from all analyzers, but can receive the light from only one single analyzer at a time. By means of corresponding mechanics, the various monochromators consisting each of a focussing analyzer crystal with entrance and exit gap, are successively brought between the sample and the detector and thus the individual parts of the spectrum are recorded successively.
This arrangement has the disadvantage that on the one hand only one single spectral line can be measured at a time. Therefore the spectrometer works extremely slowly compared to other known wavelength-dispersive arrangements like e.g. the above-mentioned "MRS 4000". Although the same detector is used for a variety of different wavelength ranges, its energy dispersion which is of course usually present is not utilized. Furthermore, owing to its moveable parts the device according to WO 97/05474 has the disadvantage of a high mechanical effort, and during operation the complicated mechanics will frequently lead to operational faults.
In contrast thereto, it is the object of the present invention to present a spectrometer for the simultaneous measurement of several spectral lines with the initially described features and which on the one hand achieves the high resolution of known wavelength-dispersive arrangements in combination with relatively short measuring times by simultaneous measurements of different wavelength ranges but which on the other hand considerably reduces the complexity of the apparatus, in particular the number of detectors and associated measuring electronics without having to increase the constructional effort with respect to the mechanical apparatus to a considerable extent.